Nonlinear Quantum Electrodynamics in Dirac Materials

Plasmon-induced magnetic anapole mode assisted strong field enhancement

Optical metamaterials, sensing, nonlinear optics, and surface-enhanced spectroscopies have witnessed the remarkable potential of the anapole mode. While dielectric particles with a high refractive index have garnered significant attention in recent years, the exploration of plasmonic anapole modes with intense localized electric field enhancements in the visible frequency range remains limited. In this study, we present a theoretical investigation on the relationship between the strongest near-field response and magnetic anapole modes, along with their substantial enhancement of Raman signals from probing molecules. These captivating findings arise from the design of a practical metallic oblate spheroid-film plasmonic system that generates magnetic anapole resonances at frequencies within the visible-near-infrared range. This research not only sheds light on the underlying mechanisms in a wide range of plasmon-enhanced spectroscopies but also paves the way for innovative nano-device designs.

Orbital magnetization of three-dimensional Dirac electrons in the quantum limit

In this study, we evaluated the dependence of magnetization of three-dimensional Dirac electrons in the quantum limit on the magnetic field and temperature. The magnetization was calculated by differentiating the free energy with respect to the magnetic field. The field and temperature dependence of the chemical potential were entirely considered under the canonical ensemble condition. The total magnetizationMconsisted of two contributions from the conductionMcand valenceMvbands.Mvwas insensitive to temperature and exhibited sub-linear field dependence, which is consistent with the previous research on Dirac electrons. By contrast,Mcwas sensitive to both temperature and magnetic field, yielding a non-trivial contribution to the totalM. As a result, the properties of totalMchanged at approximatelykBT≃EF, whereEFis the Fermi energy measured from the band bottom andkBis the Boltzmann constant. At low temperatureskBT≲EF,Mexhibited sub-linear field dependence, whereasMexhibited super-linear field dependence at high temperatureskBT≳EF. This qualitative change in the field dependence ofMwill play a significant role in the magnetization of Dirac electrons with smallEF.